Oil field operators seek as much information as possible regarding parameters and conditions encountered downhole. Such information typically includes characteristics of the earth formations traversed by the borehole, and data relating to the size and configuration of the borehole itself. The collection of information relating to conditions downhole, which commonly is referred to as “logging,” can be performed by several methods including wireline logging, “logging while drilling” (LWD), drillpipe conveyed logging, and coil tubing conveyed logging.
In wireline logging, a probe or “sonde” is lowered into the borehole after some or all of the well has been drilled. The sonde hangs at the end of a long cable or “wireline” that provides mechanical support to the sonde and also provides an electrical connection between the sonde and electrical equipment located at the surface of the well. In accordance with existing logging techniques, various parameters of the earth's formations are measured and correlated with the position of the sonde in the borehole as the sonde is pulled uphole.
In LWD, the drilling assembly includes sensing instruments that measure various parameters as the formation is being penetrated. While LWD techniques allow more contemporaneous formation measurements, drilling operations create an environment that is generally hostile to electronic instrumentation and sensor operations.
In drillpipe- or coil tubing-conveyed logging, sensing instruments are mounted on a tubing string, which moves the instrument package through an existing borehole. The tubing string enables logging of horizontal well bores without requiring the sensing instruments to tolerate the hostile drilling environment. Typically, the measurement data is stored in internal memory and recovered along with the instrument package.
Most logging tools acquire a single depth-dependent measurement, enabling a driller to see the measurement of temperature, pressure, density, resistivity, natural gamma radiation, borehole diameter, etc., as a function of depth. A few existing logging tools offer measurements as a function of depth and rotational angle, enabling a driller to see, e.g., an image of the borehole wall. A very few existing logging tools offer measurements as a function of depth and radial distance from the borehole (e.g., induction tools having multiple depths of investigation). While each of these tools is useful to some degree, they leave the driller with an incomplete picture of the situation downhole.
While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the disclosure, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the scope of the appended claims.